Communication method of a terminal  and an access point for power saving

ABSTRACT

Provided is a communication technology of an access point and a terminal that may decrease power consumption by changing an operation state of the terminal from an awake state to a sleep state when a data stream to be transmitted to the terminal is absent or has completed in a transmission opportunity (TXOP) duration.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This present application is a continuation of U.S. patent applicationSer. No. 15/153,994 filed May 13, 2016, which is a continuation of U.S.patent application Ser. No. 14/529,521 filed Oct. 31, 2014, now U.S.Pat. No. 9,344,965, which is a continuation of U.S. patent applicationSer. No. 13/043,643 filed Mar. 9, 2011, now U.S. Pat. No. 8,904,207,which claims the benefit under 35 U.S.C. § 119(e) of U.S. ProvisionalApplication No. 61/412,489, filed on Nov. 11, 2010, and U.S. ProvisionalApplication No. 61/417,528, filed on Nov. 29, 2010, both of which werefiled in the United States Patent and Trademark Office, and claims thebenefit under 35 U.S.C. § 119(a) of India Patent Application No.622/CHE/2010, filed on Mar. 9, 2010, and No. 2361/CHE/2010, filed onAug. 17, 2010, both of which were filed in the Intellectual PropertyOffice of India, and Korean Patent Application No. 10-2011-0014065,filed on Feb. 17, 2011, in the Korean Intellectual Property Office, theentire disclosures of which are incorporated herein by reference for allpurposes.

BACKGROUND 1. Field

The following description relates to communication methods and aterminal and an access point for power saving.

2. Description of Related Art

Mobile terminals such as smart phones allow a user to simultaneouslyperform a variety of functions, for example, making a call, playing amotion picture, playing back a music file, viewing a digital multimediabroadcasting (DMB), a digital camera function, Bluetooth, wirelessInternet access, and the like, using a single terminal.

In addition, as the data rate of a mobile communication networks,Bluetooth, wireless Internet, and the like, increases, power consumptionof a terminal may also increase. Accordingly, there is a desire for acommunication method that may employ a high capacity battery for aterminal, and may decrease power consumption by the terminal.

SUMMARY

In one general aspect, there is provided a communication method of aterminal in a wireless network comprising an access point and aplurality of terminals, the method including: setting a power managementmode of the terminal to a power saving mode during a transmissionopportunity (TXOP) duration in which the access point transmits at leastone frame comprising data streams to the plurality of terminals,receiving information from the access point, and determining anoperation state of the terminal in the power saving mode by determiningwhether at least one predetermined criterion is satisfied based on theinformation received from the access point.

The method may further comprise transmitting information associated withthe power management mode to the access point.

The method may further comprise determining whether to change theoperation state of the corresponding terminal based on whether at leastone of the predetermined criterion is satisfied, using an enabling bitincluded in each of the at least one frame transmitted from the accesspoint.

The method may further comprise prior to setting, attempting to operatein the power saving mode by transmitting, to the access point, a framein which the power management mode is set to the power saving mode, andreceiving, from the access point, an acknowledgment (ACK) as a responsewith respect to the frame in which the power saving mode is set to thepower saving mode, wherein the setting comprises setting the powermanagement mode to the power saving mode during the TXOP duration basedon whether the ACK is received from the access point.

The method may further comprise receiving, from the access point, a TXOPsetting frame comprising information associated with the TXOP duration,determining whether the terminal is a terminal to receive a data streamduring the TXOP based on the TXOP setting frame, and transmitting aresponse frame with respect to the TXOP setting frame based on thedetermination result.

The operation state of the terminal may comprise one of an awake stateand a sleep state, and the determining may comprise determining whetherat least one of the predetermined criterion is satisfied based oninformation received from the access point, and changing the operationstate of the corresponding terminal from the awake state to the sleepstate in response to at least one of the predetermined criterion beingsatisfied.

The predetermined criterion may comprises a first criterion, a secondcriterion, and a third criterion, and if a group ID of the groupindicates that the corresponding terminal is not a member of the group,the first criterion may be satisfied, if the group ID indicates that thecorresponding terminal is a member of the group, and if a data streamcorresponding to the corresponding terminal is not to be transmittedfrom the access point during the TXOP, the second criterion may besatisfied, and if the corresponding terminal receives an indicatorindicating that there are no more additional data streams to betransmitted to the terminal during the TXOP, the third criterion may besatisfied.

The method may further comprise maintaining the operation state of thecorresponding terminal in a sleep state for the remainder of the TXOPduration after terminating receiving of the data stream according to theindicator, or after transmitting, to the access point, a block ACK withrespect to the data stream.

In another aspect, there is provided a communication method of an accesspoint in a wireless network comprising the access point and a pluralityof terminals, the method including: transmitting, to the plurality ofterminals, information associated with a transmission opportunity (TXOP)duration in which the access point obtains a TXOP with respect to achannel, in response to at least one terminal setting a power managementmode to the power saving mode during the TXOP duration, transmittinginformation for the at least one terminal to use to determine anoperation state of the at least one terminal in power saving mode, andtransmitting the data streams to the terminals during the TXOP durationbased on the operation state of each of the terminals in the powersaving mode.

The method may further comprise transmitting, to the terminals,information about whether the access point is capable of supporting thepower saving mode, or information associated with a support capabilityof the access point for the power saving mode.

The transmitting of the information may comprise transmitting, to theterminals, a TXOP setting frame comprising information associated withthe TXOP duration, and the TXOP setting frame may be generated to bedecodable by a terminal having set the power management mode to thepower saving mode and a terminal having not set the power managementmode to the power saving mode.

The method may further comprise receiving, from a terminal desiring tooperate in the power saving mode, a frame in which the power managementmode is set to the power saving mode, and in response, transmitting, tothe terminal, an acknowledgement (ACK) with respect to the frame inwhich the power management mode is set to the power saving mode.

The method may further comprise generating a group with respect to theterminals based on a quality of service (QoS) between the terminals anda channel condition, and notifying the terminals of informationassociated with members of the group.

The method may further comprise regrouping the terminals and apredetermined terminal in response to a notification of thepredetermined terminal when the predetermined terminal notifies that thepredetermined terminal enters the power saving mode.

The method may further comprise replacing, from the group, apredetermined terminal with another terminal when the predeterminedterminal enters a sleep state of the power saving modem, and notifyingthe predetermined terminal of information associated with members of thegroup updated by the replacement.

The operation state of each of the terminals may comprise one of anawake state and a sleep state, and the transmitting of the data streamsmay comprise simultaneously transmitting the data streams to terminalsin the awake state during the TXOP duration, and buffering a data streamto be transmitted to a terminal in the sleep state for an amount of timeremaining in the TXOP duration.

The method may further comprise transmitting the buffered data stream tothe terminal in the sleep state when the operation state of the terminalis changed from the sleep state to the awake state.

The information for the terminals to use to determine the operationstate in the power saving mode may comprise at least one of a groupidentifier (ID) of a group comprising each of the terminals, informationindicating whether a data stream corresponding to each of the terminalsis transmitted from the access point during the TXOP duration, andinformation indicating whether there is an additional data stream to betransmitted to each of the terminals is during the TXOP.

The method may further comprise generating an indicator indicatingwhether there is an additional data stream to be transmitted to acorresponding terminal is during the TXOP.

The generating may comprise generating an indicator indicating thatthere is no additional data stream to be transmitted to thecorresponding terminal using a preamble of a packet to be transmitted tothe corresponding terminal or a header of a media access control (MAC)frame to be transmitted to the corresponding terminal.

In another aspect, there is provided a computer-readable storage mediumcomprising program instructions to cause a computer to implement amethod including transmitting, to the plurality of terminals,information associated with a transmission opportunity (TXOP) durationin which the access point obtains a TXOP with respect to a channel, inresponse to at least one terminal setting a power management mode to thepower saving mode during the TXOP duration, transmitting information forthe at least one terminal to use to determine an operation state of theat least one terminal in power saving mode, and transmitting the datastreams to the terminals during the TXOP duration based on the operationstate of each of the terminals in the power saving mode.

In another aspect, there is provided a terminal including a receiverconfigured to receive one or more data frames from an access pointduring a transmission opportunity (TXOP) of the access point, acontroller configured to determine whether one a of a plurality ofcriterion is satisfied based on data included in the data frame receivedfrom the access point, and a power management unit configured to adjustthe power mode of the terminal, wherein, if the controller determinesthat one of the criterion of the plurality of criterion is satisfied,the power management unit adjusts the power mode of the terminal into apower saving mode for the duration of the TXOP.

The first criterion may be satisfied when a group ID of a data frameindicates that the corresponding terminal is not a member of the groupfor the TXOP.

If a group ID of the data frame indicates that the correspondingterminal is a member of the group, the second criterion may be satisfiedif a number of state time space (N_(STS)) bit included in a very highthroughput signal (VHT-SIG) field of the data frame indicates that theterminal is not going to be transmitted data during the TXOP.

If the group ID of the data frame indicates that the correspondingterminal is a member of the group, and a N_(STS) bit included in aVHT-SIG field of the frame indicates that the terminal is to betransmitted data during the TXOP, the third criterion may be satisfiedif a more data bit (MDB) included in a MAC header of the data frame orof another data frame indicates that the transmission of the data to theterminal is completed for the TXOP.

In another aspect, there is provided an access point including acontroller configured to determine whether a terminal is included in aTXOP obtained by the access point, and a transmitter configured totransmit data to the terminal that satisfies one of a plurality ofcriterion, in response to the controller determining that the terminalis not included in some portion of the TXOP.

If the controller determines that the terminal is not included in agroup of terminals that the access point is able to transmit to duringthe TXOP, the transmitter may transmit, to the terminal, a data framecomprising a group ID field that indicates that the terminal is not amember of the group for the TXOP.

If the controller determines that the terminal is included in a group ofterminals that the access point is capable of transmitting to during theTXOP, and that the access point does not have data to transmit to theterminal during the TXOP, the transmitter may transmit, to the terminal,a data frame comprising a number of state time space (N_(STS)) bitincluded in a very high throughput signal (VHT-SIG) field of the frameto indicate that the terminal is not going to be transmitted data duringthe TXOP.

If the controller determines that the terminal is included in a group ofterminals that the access point is capable of transmitting to during theTXOP, and that the access point does have data to transmit to theterminal during the TXOP, the transmitter may transmit, to the terminal,a data frame comprising a more data bit (MDB) of a MAC header set toindicate that transmission of data to the terminal is completed.

In another aspect, there is provided a terminal including a controllerconfigured to set a one or more bits of a capability element of a VHTcontrol frame to indicate a power management mode of the terminal, and atransmitter configured to transmit, to an access point, a data frameincluding the VHT control frame indicating the power management mode ofthe terminal.

The power management modes may comprise a power saving mode in which theterminal continuously sleeps, a non-power save mode (non-TXOP PS mode)in which the terminal remains continuously awake, and a power save mode(TXOP PS mode) in which the terminal may switch from an awake state to adoze state in which the terminal sleeps, and the one or more bits of thecapability element may be set to indicate whether the terminal is in thepower saving mode, the non-TXOP PS mode, or the TXOP PS mode.

Other features and aspects may be apparent from the following detaileddescription, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an example of an operation state of aterminal in a transmission opportunity (TXOP) power saving mode.

FIG. 2 is a flowchart illustrating an example of a communication methodof a terminal.

FIG. 3 is a flowchart illustrating an example of a communication methodof an access point.

FIG. 4 is a diagram illustrating an example of a very high throughputsignal (VHT-SIG) A field of an Institute of Electrical and ElectronicsEngineers (IEEE) 802.11 preamble.

FIG. 5 is a diagram illustrating an example of an operation of eachterminal based on a power saving mode and a group identifier (ID) of agroup changed during a TXOP.

FIG. 6 is a diagram illustrating an example of a power saving rate whena predetermined criterion for power saving is satisfied.

FIG. 7 is a flowchart illustrating another example of a communicationmethod of a terminal.

FIG. 8 is a flowchart illustrating another example of a communicationmethod of an access point.

FIG. 9 is a diagram illustrating an example of a terminal setting apower management mode to a power saving mode.

FIG. 10 is a diagram illustrating an example of a frame transmitted andreceived during a TXOP.

FIG. 11 is a diagram illustrating an example of a TXOP setting frame anda TXOP duration.

FIG. 12 is a diagram illustrating an example of a VHT capabilitieselement that may be used by an access point to express the accesspoint's power saving support capability.

FIG. 13 is a diagram illustrating an example of a VHT control field of aMAC header that may be used by a terminal to notify an access point of apower management mode of the terminal.

FIG. 14 is a diagram illustrating an example of a VHT-SIG A frame thatmay be used by an access point to allow a terminal to operate in a powersaving mode.

FIG. 15 is a diagram illustrating an example of a terminal.

FIG. 16 is a diagram illustrating an example of an access point.

Throughout the drawings and the detailed description, unless otherwisedescribed, the same drawing reference numerals should be understood torefer to the same elements, features, and structures. The relative sizeand depiction of these elements may be exaggerated for clarity,illustration, and convenience.

DETAILED DESCRIPTION

The following detailed description is provided to assist the reader ingaining a comprehensive understanding of the methods, apparatuses,and/or systems described herein. Accordingly, various changes,modifications, and equivalents of the methods, apparatuses, and/orsystems described herein may be suggested to those of ordinary skill inthe art. Also, description of well-known functions and constructions maybe omitted for increased clarity and conciseness.

In certain aspects, a terminal may be a single user multiple inputmultiple output (SU-MIMO) terminal, or a multi-user multiple inputmultiple output (MU-MIMO) terminal.

FIG. 1 illustrates an example of an operation of a terminal in atransmission opportunity (TXOP) power saving mode.

At least one terminal, for example, a reception apparatus or a stationreceiving data from an access point may maintain an active mode in orderto receive a packet or a frame transmitted to the at least one terminal.The at least one terminal may remain in the active mode in order tooverhear a packet to be transmitted to another terminal.

If there is no transmission of data corresponding to the terminal, orwhen the transmission of data to the terminal is completed, it ispossible to save standby time and a receive standby power by adjustingan operation mode or a power management mode of the correspondingterminal. For example, the terminal may switch from an awake state to asleep or doze state to conserve time and power.

Referring to FIG. 1, a power management mode of a terminal includes anactive mode 110 and a power saving (PS) mode 120. While in the activemode 110, the terminal may enter into two power management modes, anon-power save mode (non-TXOP PS mode) in which the terminal staysawake, and a power save mode (TXOP PS mode) in which the terminal mayswitch between an awake state 150 and doze state 160.

The active mode 110 is a state in which the terminals may becontinuously operating to transmit and receive data to and from anaccess point. The PS mode 120 is a state, for example, an idle state inwhich the terminal does not operate or a state in which the terminalreduces overall power consumption. A terminal operating in the PS mode120 may transmit information associated with the operation state of theterminal to the access point using a portion of bits of a control fieldof a media access control (MAC) header.

In this example, terminals operating in the active mode 110 may bedivided into terminals operating in a non-TXOP PS mode 130 and terminalsoperating in a TXOP PS mode 140.

The terminals operating in the non-TXOP PS mode 130 may maintain anawake state without a separate operation for the power saving.Accordingly, the terminals operating in the non-TXOP PS mode 130 maycontinuously consume the power for a receive standby time that is usedto wait for receiving a packet to be transmitted to correspondingterminals.

The terminals operating in the TXOP PS mode 140 may change an operationstate to an awake state 150 or to a sleep state such as a doze state160, based on whether a predetermined criterion is satisfied.

For example, the predetermined criterion may include a first criterion,a second criterion, and a third criterion. If any one of the criterionis satisfied, a terminal may switch from the awake state 150 to the dozestate 160 for the remainder of the TXOP of the access point.

For example, the first criterion may be satisfied if a group identifier(ID) of a group indicates that a corresponding terminal is not a memberof the group.

As another example, the second criterion may be satisfied if the groupID of the group indicates that the corresponding terminal is the memberof the group, however, a data stream corresponding to the terminal isnot going to be transmitted from the access point during the TXOP. Inthis example, an access point may inform the terminal that a data streamcorresponding to the terminal is not going to be transmitted from theaccess point during the TXOP by setting a number of state time space(N_(STS)) included in a very high throughput signal (VHT-SIG) field of aframe to a predetermined value, for example, a value of ‘0’.

As another example, the third criterion may be satisfied if the group IDof the group indicates the terminal is a member of the group, theterminal receives a data stream during the TXOP, however, the terminalreceives an indicator indicating that there is no additional data streamto be transmitted to the terminal during the remainder of the TXOP. Thatis, the terminal receives an indicator indicating that the data streamsent to the terminal has been completed.

In this example, the indicator indicating that there is no additionaldata stream to be transmitted to the terminal during the remainder ofthe TXOP may be a more data bit (MDB) included in a MAC header of aframe received by the terminal from the access point. For example, theMDB of the MAC header may be set to ‘0’ to indicate that no more datastreams are to be transmitted to the terminal during the TXOP. That is,the MDB included in the MAC header of the frame may be set to ‘0’ toindicate that transmission of the data stream corresponding to theterminal is completed for that respective TXOP.

A terminal satisfying any one of the aforementioned criterion may savereceive standby power for a duration of the remaining time of the TXOPby changing an operation state of the terminal from the awake state 150to the doze state 160. The TXOP duration may indicate a time duration inwhich the access point simultaneously transmits data streams to a groupof terminals over a respective channel.

A terminal may notify the access point of information associated with apower management mode of the terminal using a VHT control field of a MACheader. For example, the terminal may notify the access point of whichpower management mode the terminal is in between the non-TXOP PS mode130 and the TXOP PS mode 140. A method of the terminal notifying theaccess point of the power management of the terminal is furtherdescribed with reference to FIG. 13.

For example, a terminal may notify an access point about a powermanagement mode of the terminal using a VHT control field of a MACheader. For example, the power management mode may be the power savingmode 120, the non-TXOP PS mode 130, or the TXOP PS mode 140. Theterminal may use one or more bits of the control field to indicate whichpower saving mode the terminal is in.

In various aspects, the terminal operating in the TXOP PS mode 140 maysave power and decrease the power consumption of the terminal bychanging the operation state in the TXOP duration based on thepredetermined criterion.

Hereinafter, the TXOP PS mode 140 is referred to as a power saving mode.

FIG. 2 illustrates an example of a communication method of a terminal.The communication method of the terminal in a wireless network includingan access point and one or more terminals is described with reference toFIG. 2.

In 210, the terminal notifies the access point about whether theterminal has a capability of supporting a power saving mode.

For example, to notify the access point about whether the terminal hasthe capability of supporting the power saving mode, the terminal may usea single bit of a capability/support element of an association requestframe that is transmitted while the terminal is performing anassociation with the access point. Examples of the bit of thecapability/support element are shown in Table 1.

The terminal may verify information associated with a TXOP duration froma TXOP setting frame received from the access point.

In 220, the terminal sets a power management mode to the power savingmode during the duration of the TXOP. Prior to entering the TXOP, theterminal may determine the power management mode of the terminal asdescribed herein with reference to FIG. 1.

The duration of the TXOP may correspond to a time duration in which theaccess point may transmit at least one frame including data streams to agroup including the plurality of terminals via a respective channel. TheTXOP duration may correspond to a network allocation vector (NAV)duration.

The terminal may determine an operation state of the terminal as thepower saving mode (i.e. doze/sleep state) by determining whether apredetermined criterion is satisfied based on information received fromthe access point.

The operation state of the terminal in the power saving mode maycorrespond to one of an awake state and a sleep state.

Information received from the access point may be used when the terminaldetermines the operation state of the terminal as the power saving mode.For example, information received from the access point may include atleast one of a group ID indicating whether the terminal is a member ofthe group that may receive data from the access point, informationindicating whether a data stream corresponding to the correspondingterminal is to be transmitted from the access point during the TXOP, andinformation indicating whether there is an additional data stream to betransmitted to the terminal during the TXOP.

Whether the data stream corresponding to the terminal is going to betransmitted from the access point during the TXOP may be verified basedon an N_(STS) field included in a VHT-SIG-A field. The terminal mayverify whether a data stream to be transmitted to the terminal ispending in the access point, based on the N_(STS).

For example, the N_(STS) may be set to ‘0’ to indicate that the there isno data stream to be transmitted to the corresponding to the terminalfrom the access point during the TXOP. As another example, the N_(STS)may be set to ‘0’ to indicate that there is a data stream correspondingto the terminal that is to be transmitted from the access point duringthe TXOP duration. As another example, the N_(STS) may be set to a valueexcluding ‘0’ to indicate that there is a data stream to be transmittedto the corresponding terminal from the access point during the TXOPduration.

Whether there is an additional data stream to be transmitted to theterminal during the TXOP may be verified using, for example, an MDB of acontrol field of a MAC header. For example, the MDB may be set to ‘0’ toindicate that there is no additional data stream to be transmitted tothe terminal during the TXOP. As another example, the MDB may be set to‘1’ to indicate that an additional data stream will be sent to theterminal. As another example, the MDB may be set to ‘1’ to indicate thatthere are no more data streams to be transmitted to the terminal duringthe TXOP.

In 230, the terminal receives information associated with the TXOPduration from the access point.

The terminal may verify information associated with the TXOP duration bychecking a duration field of a request to send (RTS) frame received fromthe access point. In this example, an RTS/clear to send (CTS) frame maybe initially transmitted before the TXOP duration starts and theterminal may receive information associated with the TXOP duration.

To determine the TXOP duration, the terminal may utilize the RTS/CTSframe, a self CTS frame, a duration field, and the like.

A duration field of the RTS/CTS frame may correspond to a TXOP timeperiod.

For example, the self CTS frame may be used for a downlink MU-MIMO. Theaccess point may transmit the self CTS frame prior to transmitting dataframes to the terminals included in the group. A duration bit of theself CTS frame may indicate a TXOP duration.

As another example, a duration value may be expressed by bits of aVHT-SIG-A field of a preamble.

In 240, the terminal determines whether a predetermined criterion issatisfied based on information received from the access point.

In response to the predetermined criterion being satisfied, the terminalchanges the operation state of the corresponding terminal from the awakestate to the sleep state for the remainder of the TXOP duration, in 250.In response to changing the operation state to the sleep state, forexample, the terminal may decrease power consumption such as the receivestandby power consumption and the data receive power consumption bymaintaining the sleep state for the remainder of the TXOP duration.

In response to the predetermined criterion not being satisfied, in 260the terminal maintains the operation state of the terminal as the awakestate.

For example, the predetermined criterion may include a first criterion,a second criterion, and a third criterion, as described with referenceto FIG. 1.

When the group ID of the group indicates that the terminal is not amember of the group, the first criterion may be satisfied. For example,it may be assumed that the terminal is a terminal 4, and a group havinga group ID of ‘A’ includes a terminal 1, a terminal 3, and a terminal 5.In this example, because terminal 4 is not included in the group A, theterminal is not a member of the group A. Accordingly, the firstcriterion is satisfied.

When the group ID of the group indicates that the corresponding terminalis a member of the group, however, a data stream corresponding to theterminal is not going to be transmitted from the access point during theTXOP, the second criterion may be satisfied. In this example, the accesspoint may indicate that there is no data stream to be transmitted to thecorresponding terminal from the access point during the TXOP based on avalue of an N_(STS) field included in a VHT-SIG-A field of a frame.

As another example, the third criterion may be satisfied if the group IDof the group indicates the terminal is a member of the group, theterminal receives a data stream during the TXOP, but the terminalreceives an indicator indicating that there is no additional data streamto be transmitted to the terminal during the TXOP. In this example, theindicator may be an MDB of a MAC header.

FIG. 3 illustrates an example of a communication method of an accesspoint. The communication method of the access point in a wirelessnetwork including the access point and one or more terminals isdescribed with reference to FIG. 3.

The access point may transmit a frame to a terminal, or may buffer theframe during a TXOP. Accordingly, the access point may determine anoperation of the access point by receiving information associated with acurrent operation state of the terminal through association with theterminal.

In 310, the access point transmits, to one or more terminals,information about whether the access point is capable of supporting thepower saving mode and information associated with a support capabilityof the access point for the power saving mode.

For example, the access point may notify the terminal about whether theaccess point is capable of supporting the power saving mode and thesupport capability of the access point, using an information element ora capability element of a probe response frame or a beacon frame. Inthis example, whether the access point is capable of supporting thepower saving mode may correspond to whether the access point is capableof performing association with a terminal operating in the power savingmode.

A method of indicating the support capability of the access point forthe power saving mode is further described with reference to FIG. 12. In320, the access point transmits information associated with the TXOPduration to the terminals. For example, the TXOP duration may correspondto a time duration in which the access point obtaining a TXOP withrespect to the channel may transmit at least one frame including datastreams to one or more terminals.

The terminals may be made aware of information associated with the TXOPduration before entering the sleep state. For example, the terminals maybe informed about an amount of remaining time for the TXOP, and theaccess point may transmit corresponding information to the terminals.

The terminals may be made aware of information about whether anadditional data stream corresponding to each of the terminals, that is,whether there is an additional data stream to be transmitted to each ofthe terminals during the TXOP. Accordingly, the access point mayprovide, to the terminals, information about whether there is anadditional data stream to be transmitted to each of the terminals duringthe TXOP, using information used to determine the operation state.

In response to at least one terminal setting the power management modeto the power saving mode during the TXOP, the access point may transmitinformation to be used by the at least one terminal to determine theoperation state of the terminal in the power saving mode, in 330. Theoperation state in the power saving mode may correspond to one of anawake state and a sleep state or doze state.

Information used when each of the at least one terminal determines theoperation state in the power saving mode as one of the awake state andthe sleep state may include at least one of an ID of a group includingeach of the terminals, information indicating whether there is a datastream to be transmitted to each of the terminals from the access pointduring the TXOP, and information indicating whether there is anadditional data stream to be transmitted to the terminals during theTXOP.

For example, whether there is a data stream to be transmitted to each ofthe terminals from the access point during the TXOP may be verified froman N_(STS) field included in a VHT-SIG-A field.

As another example, whether there is an additional data stream to betransmitted to each of the terminals during the TXOP may be verifiedfrom an MDB of a control field.

In 340, the access point simultaneously transmits data streams to one ormore terminals during the TXOP duration based on an operation state ofeach of the terminals.

For example, in 340, the access point may simultaneously transmit datastreams to terminals in the awake state from among the terminals duringthe TXOP. For example, if a data stream is to be transmitted to aterminal that is in the sleep state during the remaining time of theTXOP duration, the access point may buffer the data stream to betransmitted.

In this example, ‘simultaneously’ transmitting the data streams mayindicate that the data streams are simultaneously transmitted in aspatial aspect or are transmitted using an MU-MIMO) communication, andmay not indicate that transmission of data streams corresponding to atleast one terminal simultaneously starts and is simultaneouslycompleted.

For example, the access point may not transmit a data streamcorresponding to a terminal satisfying a predetermined criterion, sothat the terminal satisfying the predetermined criterion may maintainthe operation state as the sleep state for the remainder of the TXOP.

Whether the terminal satisfies the predetermined criterion may bedetermined based on information used to determine the operation state.

The predetermined criterion may include a first criterion, a secondcriterion, and a third criterion as described herein. Descriptionsrelated thereto may refer to the descriptions described above withreference to FIGS. 1-3.

In response to an operation state of a terminal being changed from thesleep state to the awake state, the access point may transmit thebuffered data stream to the terminal. In this example, if the TXOPduration ends, the access point may automatically recognize that theoperation state of the corresponding terminal is changed from the sleepstate to the awake state. As another example, the terminal may transmita power save-poll message to the access point to inform the access pointthat the terminal is in the awake mode.

The power save-poll message may be a message that the terminal in thesleep state transmits in order to notify the access point of that theoperation state of the terminal is changed from the sleep state to theawake state.

For example, when the terminal desires to operate in the power savingmode, the terminal may transmit, to the AP, a frame in which a powermanagement mode is set to the power saving mode. The AP may transmit anACK to the terminal in response to the frame.

In response, the AP transmits, to the terminal, information about theTXOP such as the Group ID, whether there is a data stream for theterminal, and whether there is an additional data stream for theterminal. The terminal may determine whether the predetermined criterionis satisfied based on the information. In this example, because theinformation is transmitted from the AP, the AP also may know whether thepredetermined criterion is satisfied for each respective terminal.

Accordingly, even if the terminal does not transmit additionalinformation that the terminal is going to enter into the sleep state,the AP may recognize that the terminal is going to enter into the sleepstate.

In a MU-MIMO 802.11 network, the access point may group, into a singlegroup or a plurality of groups, one or more terminals to which theaccess point may simultaneously transmit data. The access point mayconfigure the single group or the plurality of groups with respect tothe terminals based on a predetermined criterion, for example, a qualityof service (QoS) requirement, a channel condition, and the like. Theaccess point may notify the terminals of information associated withmembers of a group.

The access point may notify the terminals of information associated withmembers of the group using, for example, a management frame. A grouphaving a predetermined group ID may include a set of terminals includedin a corresponding cell.

The access point may assign a group ID independently from a TXOPtransmission, that is, a transmission of a data frame between TXOPdurations, instead of in the TXOP duration.

In response to a predetermined terminal entering the sleep state of thepower saving mode, the access point may replace the predeterminedterminal from the group with another terminal corresponding to data tobe transmitted. In response, the access point may notify the terminalsof information associated with the new member, that is, another terminalof the group that is updated by the replacement.

In response to the predetermined terminal notifying that thepredetermined terminal enters the power saving mode, the access pointmay regroup the terminals and the predetermined terminal.

The aforementioned regrouping may be used when the predeterminedterminal operates in the power saving mode for at least one TXOP.

The regrouping may enable the access point to transmit data to anotherterminal rather than to transmit a packet or a frame to a terminal thatthe access point does not have data to transmit to.

For example, in response to the TXOP duration being truncated orshortened, the access point may buffer a frame for terminals enteringthe power saving mode for an amount of remaining time of the duration ofthe TXOP.

Table 1 illustrates examples of bits used for a control field and aninformation element for power saving according to various aspects.

TABLE 1 number Entity of bits Description 1 Information element ofinformation 1 ‘0’: may be used to indicate that access element field ofbeacon frame point does not support power saving mode. ‘1’: may be usedto indicate that the access point supports power saving mode. 2Information element of 1 ‘0’: may be used to indicate that terminalcapabilities/support field of does not support power saving mode.association request frame ‘1’: may be used to indicate that terminalsupports power saving mode. 3 Control field of MAC header 1 ‘0’: may beused to indicate that power management mode is not set to power savingmode. ‘1’: may be used to indicate that power management mode is set topower saving mode.

In Table 1, the power saving mode may indicate a downlink MU TXOP powersaving mode. It should be appreciated that the values such as ‘0’ and‘1’ shown in Table 1 are merely for purposes of example, and othervalues may be used to perform the same notifications. For example, ‘1’may be used to indicate that access point does not support power savingmode.

FIG. 4 illustrates an example of a very high throughput signal (VHT-SIG)A field of an Institute of Electrical and Electronics Engineers (IEEE)802.11 preamble.

Referring to FIG. 4, a duration field 410 may include 12 bits, and mayinclude information associated with a TXOP duration, for example, alength of a TXOP duration and the like.

A group ID field 430 may include 14 bits, and may include group ID bits431, N_(STS) fields 433 and 435, and R_(svd) bits 437.

For example, the group ID bits 431 may include three bits, four bits,and the like, and may notify each of terminals of a group ID thatidentifies each of the terminals in the group.

For example, the N_(STS) fields 433 and 435 may include nine bits, andmay be used to verify whether a data stream is to be transmitted to theterminals during a TXOP.

The N_(STS) field 433 including lower three bits may indicate a numberof space time streams to be transmitted to terminals included as membersof the group in a corresponding frame. When a terminal k is not areceiver of an MU-MIMO packet or a frame, the N_(STS) field 433 may beexpressed by N_(STS)_k=‘0’ with respect to the terminal k.

For example, it may be assumed that a group ID of a corresponding groupis ‘1’ and terminals A, B, C, and D are included in the correspondinggroup. When N_(STS)=(0, 2, 3, 1), it may indicate that, in acorresponding frame, zero space time streams are going to be transmittedto the terminal A, two space time streams are to be transmitted to theterminal B, three space time streams are to be transmitted to theterminal C, and a single space time stream is to be transmitted to theterminal D. In this example, N_(STS)=(0, 2, 3, 1) indicates that thecorresponding frame is transmitted to the terminals B, C, and D that aremembers of the group having the group ID ‘1’.

The N_(STS) field 435 including upper six bits may be reused when thegroup ID is ‘0’. The N_(STS) field 435 may be used for power saving. Anexample of the N_(STS) field 435 used for the power saving mode isfurther described with reference to FIG. 14.

The R_(svd) bits 437 may include a single bit. For example, if theR_(svd) bits 437 is ‘1’ and values of the N_(STS) fields 433 and 435 are‘0’, it may indicate that data is absent in a data frame for apredetermined terminal included in a predetermined group. That is, itmay indicate ‘no data’, and may indicate ‘no more data’ for a terminalfor the remaining amount of time in the TXOP duration.

A cyclic redundancy check (CRC) field 450 may include eight bits, andmay be used for an error detection to verify a reliability with respectto data of a corresponding frame.

A tail field 470 may include six bits, and may be added to an end of thecorresponding frame.

FIG. 5 illustrates an example of an operation of a plurality ofterminals based on a power saving mode and a group ID of a group changedduring a TXOP.

In this example, STA may indicate, for example, a terminal, or astation, and AP may indicate, for example, an access point.

Referring to FIG. 5, an STA (1) 501, an STA (2) 502, an STA (3) 503, andan STA (4) 504 have a power management mode of ‘1’ (i.e. TXOP PS mode140 shown in FIG. 1), and an STA (5) 505 and an STA (6) 506 have a powermanagement mode of ‘0’ (i.e. non-TXOP PS mode 130 shown in FIG. 1). Asdescribed above with reference to Table. 1, when the power managementmode is ‘1’, it may indicate that a corresponding terminal operates inthe power saving mode. When the power saving mode is ‘0’, it mayindicate that the corresponding terminal operates in a mode excludingthe power saving mode.

Table 2 shows group IDs of frames to be transmitted from an AP 500 tothe terminals during the TXOP, and terminals that are members of acorresponding group. Table 2 shows information associated with aposition of a corresponding terminal in a corresponding group.

TABLE 2 Position 1 Position 2 Group ID 1 STA1, STA3, STA5 STA2, STA4,STA6 Group ID 2 STA1, STA2 STA3, STA4 Group ID 3 STA2, STA3 STA4, STA5Group ID 4 STA4, STA5 STA6

Frame (1) 510 includes a group ID 511 of GID=1, a data field 513 withrespect to the STA (1) 510 positioned in a position 1, and a data field515 with respect to the STA (2) 502 positioned in a position 2.Referring to frame (1) 510, N_(STS)s=1, 1 which in this exampleindicates that there is data to be transmitted to two terminals includedin the group ID 511 of frame (1) 510.

The STA (1) 501 and the STA (2) 502 may receive data of frame (1) 510,and transmit block acknowledgements (BAs) 591 and 592 in response toframe (1) 510. In this example, referring to the data field 513 withrespect to the STA (1) 501, more bit=‘0’. In this example, the STA (1)501 operates in the power saving mode, and thus, may enter a sleep stateafter transmitting the BA 591 for the remainder of the TXOP. Referringto the data field 515 with respect to the STA (2) 502, more bit=‘1’ andthus, STA (2) 502 remains in an awake state. In this example, ‘more bit’corresponds to an MDB and the operation of the corresponding terminalbased on the more bit may refer to descriptions made above withreference to the MDB.

Frame (2) 530 includes a group ID 531 of GID=2, a data field 535 withrespect to the STA (2) 502 positioned in the position 1, and a datafield 533 with respect to the STA (3) positioned in the position 2.Referring to frame (2) 530, N_(STS)=1, 1, which in this exampleindicates that there is data to be transmitted to two terminals includedin the group ID 531 of frame (2) 530.

The STA (3) 503 and the STA (2) 502 may receive data of frame (2) 530,and transmit BAs 593 and 595 in response to frame (2) 530. Referring tothe data field 533 with respect to the STA (3) 503, more bit=‘0’. Inthis example, the STA (3) 503 operates in the power saving mode, andthus, may enter the sleep state after transmitting the BA 595 for theremainder of the TXOP. Referring to the data field 535 with respect tothe STA (2) 502, more bit=‘1’ and thus, the STA (2) 502 remains in theawake state.

In this example, terminals, for example, the STA (4) 504, the STA (5)505, and the STA (6) 506, that do not receive a frame during the TXOPduration may be in an ‘on’ state between frame transmission durations inorder to verify whether a corresponding frame is transmitted to acorresponding terminal.

Frame (3) 550 includes a group ID 551 of GID=3, and a data field 553with respect to the STA (2) 502 positioned included in the position 1.Referring to frame (3) 550, N_(STS)=1, 0, which in this exampleindicates that there is data to be transmitted to a single terminalincluded in the group ID 551 of the frame (3) 550, and also indicatesthat data is not going to be transmitted to another terminal in thegroup ID 551. Referring to the data field 553 with respect to the STA(2) 502, more bit=0. As a result, the STA (2) 502 may receive thecorresponding data and transmit a BA 594 to the AP 500 and then enterthe sleep state for the remainder of the TXOP.

In this example, STA (4) 504 is positioned in the position 2 of thegroup ID 3. However, because N_(STS)=1, 0 in frame (3) 550, thisindicates that no data is to be transmitted to the STA (4) 504. In thisexample, a second criterion is satisfied and the STA (4) 504 may entersleep mode for the remainder of the TXOP. That is, the STA (4) 504 mayenter the sleep state after receiving a preamble of frame (3) 550.

Frame (4) 570 includes a group ID 571 of GID=4, a data frame 575 withrespect to the STA (5) 505 positioned in the position 1, and a dataframe 573 with respect to the STA (6) 506 positioned in the position 2.Referring to the frame (4) 570, N_(STS)=1, 1, which in this example isused to indicate that there is data to be transmitted to two terminalsincluded in the group ID 571 of the frame (4) 570.

The STA (5) 505 and the STA (6) 506 may receive data of the frame (4)570, and transmit BAs 596 and 597 in response to the frame (4) 570.Referring to the data field 573 with respect to the STA (6) 506, morebit=0, however, the STA (6) 506 does not operate in the power savingmode. Accordingly, after transmitting the BA 597, the STA (6) 506 maystill remain in the awake state.

FIG. 6 illustrates an example of a power saving rate when apredetermined criterion for power saving is satisfied.

Referring to FIG. 6, MU-BA may include a short inter-frame space (SIFS)and a BA from each of a plurality of terminals for each MU-BA phase. Asingle extra SIFS may be inserted between an end of the BA and a startof a subsequent frame.

$\begin{matrix}{\left. {{{No}.\mspace{14mu} {of}}\mspace{14mu} {frames}\mspace{14mu} (N)}\rightarrow N \right. = \left\lfloor \frac{3.008\mspace{14mu} {ms}}{T_{Frame} + T_{BA}} \right\rfloor} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$

In Equation 1, N corresponds to a number of frames that have a unit sizeavailable in 3.008 ms. T_(Frame) corresponds to a frame duration and mayhave a value of, for example, 0.5 ms, 1 ms, 1.5 ms, and the like. T_(BA)corresponds to a duration of an uplink MU-BA phase. T_(BA) may beexpressed by 4*(28 μs+SIFS)+1*SIFS.

T _(TXOP) =N*(T _(Frame) +T _(BA))  [Equation 2]

In Equation 2, T_(TXOP) ⁽¹⁾ corresponds to the TXOP duration.

A power saving rate PS_(TXOP) ⁽¹⁾ of a case in which the aforementionedthird criterion is satisfied may be expressed by Equation 3. In theexample of FIG. 6, the third criterion is satisfied in CASE 1.

$\begin{matrix}{{PS}_{TXOP}^{(1)} = {\frac{T_{{OFF}\; 1}}{T_{TXOP}} = \frac{T_{TXOP} - {n*\left( {T_{Frame} + T_{BA}} \right)}}{T_{TXOP}}}} & \left\lbrack {{Equation}\mspace{14mu} 3} \right\rbrack\end{matrix}$

In Equation 3, T_(OFF) corresponds to a duration for a terminal in thepower saving mode. In this example, ‘n’ may have values from ‘0’ to N,and corresponds to a number of frames that are to be transmitted to theterminal.

A power saving rate PS_(TXOP) ⁽²⁾ of a case in which the aforementionedfirst criterion and second criterion are satisfied may be expressed byEquation 4. In this example, the first and second criterion aresatisfied in CASE 2 of FIG. 6.

Equation 4 expresses a power saving rate when a group ID indicates thata corresponding terminal is not a member of a corresponding group, orwhen the group ID indicates that the corresponding terminal is a memberof the corresponding group, however, there is no data stream to betransmitted to the corresponding terminal from an access point duringthe TXOP.

A case in which there is no data stream to be transmitted to thecorresponding terminal during the TXOP may be a case in which theN_(STS) included in a VHT-SIG-A field of a frame transmitted to thecorresponding terminal is set to ‘0’.

$\begin{matrix}{{PS}_{TXOP}^{(2)} = {\frac{T_{{OFF}\; 2}}{T_{TXOP}} = \frac{T_{TXOP} - {n*\left( {T_{Frame} + T_{BA}} \right)} - T_{{VHT} - {SIG} - A}}{T_{TXOP}}}} & \left\lbrack {{Equation}\mspace{14mu} 4} \right\rbrack\end{matrix}$

In Equation 4, T_(VHT SIG-A) corresponds to a time to decode VHTSIG-A=28 μs.

FIG. 7 illustrates another example of a communication method of aterminal.

For example, the terminal may correspond to a terminal from among one ormore terminals having a power management mode as an active mode. Duringa TXOP, streams corresponding to the terminals may be simultaneouslytransmitted from an access point.

In 710, the terminal determines to operate in a power saving mode. Inresponse to determining to operate in the power saving mode, in 720 theterminal transmits, to the access point, a frame in which a powermanagement mode is set to the power saving mode. By setting the powermanagement mode to the power saving mode, the terminal indicates to theaccess point that the terminal desires to operate in power saving mode.

For example, the power management mode may be set to the power savingmode by setting a field or a bit indicating whether the power savingmode is used in a frame transmitted to the access point. For example, acapabilities/support field of an association request frame may be set toa value of ‘1’.

In response to determining that the terminal is not to operate in thepower saving mode, for example, when the terminal determines to operatein the non-TXOP PS mode 130 of FIG. 1, the terminal may maintain theoperation state as an awake state, in 780.

In 730, the terminal determines whether an ACK is received from theaccess point in response to the frame in which the power management modeis set to the power saving mode.

When the ACK is not received from the access point in 730, the terminalmaintains the operation state as the awake state, in 780. For example,when the ACK is not received from the access point, the terminal may notoperate in the power saving mode.

When the ACK is received from the access point, the terminal sets thepower management mode to the power saving mode during the remainder ofthe TXOP, in 740.

In 750, the terminal receives, from the access point, a TXOP settingframe including information associated with the TXOP duration.

For example, the TXOP setting frame may be generated to be decodable byboth a terminal having set the power management mode to the power savingmode, and a terminal having not set the power management mode to thepower saving mode.

A period in which the terminal may receive the TXOP setting frame maynot be limited by the aforementioned order, and thus, may be changed fora process of communicating with the access point.

In this example, the terminal may determine whether the terminalcorresponds to a terminal that is to receive a corresponding data streambased on the TXOP setting frame received from the access point. Based onthe determination result, the terminal may transmit, to the accesspoint, a response frame with respect to the TXOP setting frame.

In 760, the terminal may determine whether a predetermined criterion issatisfied based on information transmitted from the access point. Theterminal may determine the operation state of the terminal bydetermining whether the predetermined criterion is satisfied.

For example, information transmitted from the access point may includeat least one of a group ID of a group including the terminal,information about whether a data stream corresponding to the terminal isto be transmitted from the access point during the TXOP, and informationindicating whether there is an additional data stream to be transmittedto the terminal during the TXOP.

The predetermined criterion may include a first criterion, a secondcriterion, and a third criterion. When the terminal is not included inthe group of the group ID including a set of terminals within acorresponding cell, the first criterion may be satisfied. When theterminal is included in the group of the group ID, but a data streamcorresponding to the terminal is not to be transmitted from the accesspoint during the TXOP, the second criterion may be satisfied. When anindicator indicating that there is no additional data stream to betransmitted to the terminal during the TXOP, the third criterion may besatisfied.

For example, the terminal may selectively determine whether to changethe operation state of the terminal based on the first criterion and thesecond criterion, using an enabling bit included in each of framestransmitted from the access point.

In response to at least one of the predetermined criterion beingsatisfied in 760, the terminal changes the operation state of theterminal from the awake state to the sleep state, in 770. The terminalmay save receive standby power and decrease power consumption forreceiving data by maintaining the sleep state for the remainder of theTXOP.

Conversely, when the predetermined criterion is not satisfied, theterminal maintains the operation state of the terminal in the awakestate, in 780.

FIG. 8 illustrates another example of a communication method of anaccess point.

In 810, the access point receives a frame in which a power managementmode is set to a power saving mode. The frame may be received from aterminal indicating the terminal is to operate in the power saving modefrom among terminals having an active mode as the power management mode.

In 820, the access point transmits an ACK to the terminal in response tothe frame in which the power management mode is set to the power savingmode.

In 830, the access point obtains a TXOP with respect to a channel.

In 840, the access point maintains data streams corresponding toterminals that have the active mode as a power management mode.

In 850, the access point transmits information that may be used by theterminals to determine an operation state of each of the terminals.

For example, the information that may be used by the terminals todetermine the operation state of each of the terminals may include atleast one of a group ID of a group including each of the terminals thatthe access point may transmit data streams to, information about whethera data stream corresponding to each of the terminals is transmitted fromthe access point during the TXOP duration, and information indicatingwhether there is an additional data stream to be transmitted to theterminals during the TXOP.

In 860, the access point transmits the data streams to at least one ofthe terminals during the TXOP. For example, if a plurality of terminalsare in the awake mode, the access point may simultaneously transmit datastreams to the plurality of terminals.

For example, ‘simultaneously’ transmitting the data streams may indicatethat the data streams are simultaneously transmitted in a spatial aspector are transmitted using a MU-MIMO communication, and may not indicatethat transmission of data streams corresponding to at least one terminalsimultaneously starts and is simultaneously completed.

The TXOP duration may correspond to a time duration corresponding to aTXOP with respect to the channel, and may correspond to a time durationin which the access point obtaining the TXOP with respect to the channelmay transmit at least one frame including the data streams to the groupincluding the terminals. For example, the TXOP duration may indicate theamount of time that an access point has to transmit data on a respectivechannel.

Based on information used to determine the operation state, the accesspoint may not transmit a data stream to a terminal that is in a sleepstate. For example, terminals satisfying a predetermined criterion maymaintain an operation state in the sleep state for the remaining amountof the TXOP duration.

The information used to determine the operation state and the datastreams may be included in the same frame. For example, the group of thegroup ID may include the set of terminals within the corresponding cell.

The access point may transmit a frame including an enabling bit thatenables the terminal to selectively determine whether to change theoperation state of the terminal based on the first criterion and/or thesecond criterion.

In 870, the access point generates an indicator indicating whether thereis an additional data stream to be transmitted to the terminal duringthe TXOP.

For example, in 870, the access point generates the indicator indicatingthat there are no more additional data streams corresponding to theterminal that are to be transmitted during the TXOP using a preamble ofa packet transmitted to the terminal or a header of a MAC frametransmitted to the terminal. For example, the indicator may be an MDB ofthe MAC header.

In 880, the access point buffers a data stream that is to be transmittedto a terminal in the sleep state for the remainder of the TXOP duration.For example, a TXOP may be cut short for various unforeseen reasons, andthe terminal may still be in a sleep state for the remainder of the TXOPwhich was cut short. Therefore, the access point may buffer data that isto be sent to the terminal.

FIG. 9 illustrates an example of a terminal setting a power managementmode to a power saving mode.

A STA may indicate, for example, a terminal, or a station, and AP mayindicate, for example, an access point.

STA (1) 903 desiring to operate in a power saving mode may transmit, toan AP (1) 901, a frame 911 in which a power saving mode, that is, a TXOPPS mode, is set to ‘1’. In this example, setting of the power savingmode to ‘1’ may indicate that a corresponding STA sets the powermanagement mode of the corresponding STA to the power saving mode. Thecorresponding STA may use, for example, a capabilities/support field ofan association request frame to set the power management mode of the STAto indicate that the STA desires to operate in power saving mode. TheSTA (1) 903 may receive an ACK 913 from the AP (1) 901 as a response tothe frame 911.

After receiving the ACK 913, the STA (1) 903 may operate in the powersaving mode.

Similarly, an STA (2) 905 may transmit, to the AP (1) 901, a frame 915in which the power saving mode is set to ‘1’, and may operate in thepower saving mode after receiving an ACK 917 from the AP (1) 901.

The STA (1) 903 and the STA (2) 905 may be set to operate in the powersaving mode by performing the aforementioned operation as the AP (1) 901in a TXOP PS mode setting period 910.

In a TXOP duration setting period 930, the AP (1) 901, the STA (1) 903,and the STA (2) 905 may set a TXOP duration 950 using a request to send(RTS) frame 931 and a clear to send (CTS) frame 933.

The TXOP duration setting period 930 may correspond to a TXOP settingperiod which is further described later.

The RTS frame 931 and the CTS frame 933 may be used to prevent a framecollision known as a hidden node issue. A process may be initiated bytransmitting, by a node, for example, the AP (1) 901 desiring totransmit data, the RTS frame 931. In the case of a wireless environmentin which a transmission is possible because other signals being are notbeing transmitted, the STA (1) 903 corresponding to a destination nodemay transmit the CTS frame 933 as a response to the signal. The othernodes receiving the RTS frame 931 or the CTS frame 933 may solve thehidden node issue by limiting a data transmission for a predeterminedamount of time. The predetermined amount of time may be included in theRTS frame 931 and the CTS frame 933.

FIG. 10 illustrates an example of a frame transmitted and receivedduring a TXOP. In this example, the second criterion is not considered.

Referring to FIG. 10, an AP (1) 1001 and six STAs, for example, an STA(1) 1003, an STA (2) 1005, an STA (3) 1007, an STA (4) 1009, an STA (5)1011, and an STA (6) 1013 are present within a single cell or a basicservice set (BSS), and the six STAs are shown in Table 3.

TABLE 3 Apparatuses using TXOP Apparatuses using non-TXOP PS mode PSmode Data in buffer STA 1, STA 2 STA 4, STA 5, STA 6 No data STA 3 N/A

Referring to Table 3, among the six STAs, the STA (1) 1003, the STA (2)1005, and the STA (3) 1007 correspond to terminals in a power savingmode, that is, a TXOP PS mode 140 illustrated in FIG. 1.

In this example, the AP (1) 1001 has data to transmit to the STA (1)1003, the STA (2) 1005, the STA (4) 1009, the STA (5) 1011, and the STA(6) 1013.

Referring to FIG. 10, Frame (1) 1020 includes all the stations, that is,the STA (1) 1003, the STA (2) 1005, the STA (3) 1007, the STA (4) 1009,the STA (5) 1011, and the STA (6) 1013, in a group of a group IDincluded in a preamble 1021. Accordingly, after receiving Frame (1)1020, the first criterion is not satisfied for any of the STAs.

Frame (1) 1020 includes data 1023 to be transmitted to the STA (1) 1003,and data 1025 to be transmitted to the STA (4) 1009, and an MDB of theSTA (1) 1003 is set to ‘0’.

The MDB of the STA (1) 1003 is set to ‘0’ which in this exampleindicates that there is no more data to be additionally transmitted fromthe AP (1) 1001 to the STA (1) 1003. Thus, the third criterion issatisfied for STA (1) 103. Accordingly, the STA (1) 1003 may transmit ablock acknowledgement (BA) 1090 to the AP (1) 1001 and then operate inthe power saving mode until the end of the TXOP, thereby reducingstandby power consumption. An example of the power saving state is asleep state or a doze state.

After completing reception of a corresponding data stream based on theMDB, or after transmitting the BA 1090 with respect to the correspondingdata stream, the STA (1) 1003 may maintain the operation state of theSTA (1) 1003 in a sleep state for the remaining time of the TXOPduration.

Frame (2) 1040 includes the STA (2) 1005, the STA (3) 1007, and the STA(4) 1009 in a group of a group ID included in a preamble 1041, andincludes data 1043 to be transmitted to the STA (2) 1005 and data 1045to be transmitted to the STA (4) 1009.

The STA (3) 1007 in the power saving mode, that is, the TXOP PS modedoes not have data to receive from the AP (1) 1001, however, is includedin the group ID. Accordingly, the STA (3) 1007 may not enter the sleepstate. That is, in the example of FIG. 10, the STAs do not consider thesecond criterion, but only consider the first and third criterion.

In frame (2) 1040, an MDB of the STA (2) 1005 is set to ‘1’ and thus,STA (2) 1005 may remain in an awake state.

In frame (2) 1040, an MDB of the STA (4) 1009 is set to ‘0’, however,STA (4) 1009 is in non-TXOP PS mode and does not use the power savingmode. Accordingly, even after transmitting, to the AP (1) 1001, BAs 1093and 1094 in response to the frame (1) 1020 and the frame (2) 1040, theSTA (4) 1009 may remain in the awake state instead of saving power.

Frame (3) 1060 includes the STA (2) 1005 and the STA (5) 1011 in a groupof a group ID included in a preamble 1061, and includes data 1063 to betransmitted to the STA (2) 1005 and data 1065 to be transmitted to theSTA (5) 1011.

The STA (3) 1007 operating in the power saving mode is not included in agroup of a group ID of a frame (4) 1080, and therefore, the firstcriterion is satisfied for the STA (3) 1007. Thus, the STA (3) 1007 mayenter into a power saving mode for the remainder of the TXOP.

In the example of FIG. 10, operating in the power saving state mayindicate remaining in the sleep state.

In frame (3) 1060, the MDB of the STA (2) 1005 is set to ‘0’, and thus,the STA (2) may enter into a power saving state such as a sleep statefor the remainder of the TXOP duration after receiving data.

Frame (4) 1080 includes the STA (5) 1011 and the STA (6) 1013 in a groupof a group ID included in a preamble 1081, and includes data 1083 to betransmitted to the STA (5) 1011 and data 1085 to be transmitted to theSTA (6) 1013. Even though frame (4) 1080 includes the STA (3) 1007, theSTA (3) 1007 is already in the sleep state. Accordingly, the STA (3)1007 may continuously maintain the sleep state during the TXOP duration.

The STA (5) 1011 and the STA (6) 1013 may receive frame (4) 1080 and maytransmit BAs 1096 and 1097 to the AP (1) 1001.

The AP (1) 1001 may include any STAs in a group of a group ID of a frameto be transmitted. However, STAs that are in the sleep state may notreceive a corresponding frame. Accordingly, the AP (1) 1001 may bufferdata to be transmitted while a corresponding STA is in the sleep state.

FIG. 11 illustrates an example of a TXOP setting frame and a TXOPduration.

Referring to FIG. 11, an AP (1) 1101 may set a time durationcorresponding to a TXOP with respect to a channel. For example, the AP(1) 1101 may set a TXOP duration 1130 by transmitting a TXOP settingframe 1120 in a TXOP setting period 1110.

The TXOP setting frame 1120 may include information used to set the timeduration corresponding to the TXOP duration 1130. The TXOP setting frame1120 may be transmitted in a form that may be overheard by all the STAswithin a cell or a BSS. For example, the STAs may include terminalshaving set a power management mode to a power saving mode such as asleep state, and terminals having not set the power management mode tothe power saving mode such as an awake state.

For example, a multi-user precoding scheme and the like may not beapplied to the TXOP setting frame 1120. The TXOP setting frame 1120 maybe generated to be decodable by all the STAs within the cell even thoseSTAs that are in a sleep state.

The TXOP setting frame 1120 may include information about whether toapply the power saving mode, or a target reception group that is atransmission target of a frame during the corresponding TXOP duration1130. Information associated with the target reception group may includea predetermined group that has the same group ID and STAs belonging tothe predetermined group.

When the TXOP setting frame 1120 includes information associated withthe target reception group, STAs excluded from a corresponding receptiongroup may maintain the sleep state by the end of the TXOP duration 1130after receiving the TXOP setting frame 1120.

A single STA or STAs belonging to the target reception group maytransmit a response frame 1160 with respect to the TXOP setting frame1120. For example, the response frame 1160 may include a portion of orall of descriptions included in the TXOP setting frame 1120.

Accordingly, hidden nodes not receiving the TXOP setting frame 1120 mayset a TXOP. When at least one STA transmits the response frame 1160, theat least one STA may transmit the response frame 1160 according to apredetermined order and a predetermined method. Otherwise, correspondinginformation may be included in the TXOP setting frame 1120.

The TXOP setting period 1110 may be used to set the time durationcorresponding to the TXOP with respect to the channel, for example, theTXOP duration 1130.

As an example, in the TXOP setting period 1110 for setting the TXOPduration 1130, the AP (1) 1101 may transmit the TXOP setting frame 1120to an STA (1) 1103, an STA (2) 1105, an STA (3) 1107, and an STA (4)1109 within a cell.

The TXOP setting frame 1120 may be used for a corresponding terminal toreceive a corresponding data stream in the TXOP duration 1130, or tooperate in the power saving mode.

For example, the TXOP setting frame 1120 may include a preamble 1121, alegacy signal field (L-SIG) 1123, and TXOP setting information 1125 forsetting the TXOP duration 1130.

Each of the STA (1) 1103, the STA (2) 1105, the STA (3) 1107, and theSTA (4) 1109 may set the time duration corresponding to the TXOP withrespect to the channel, based on the TXOP setting information 1125.

In this example, each of the STA (1) 1103, the STA (2) 1105, and the STA(3) 1107 are to receive data from the AP (1) 1101 and may access a radiochannel in the TXOP duration 1130 to receive a packet or a frame fromthe AP (1) 1101.

However, the STA (4) 1109 is not to receive data from the AP (1) 1101and may not access the radio channel in the TXOP duration 1130.

The TXOP setting information 1125 may include information associatedwith a group of STAs to receive the data from the AP (1) 1101 among theSTA (1) 1103, the STA (2) 1105, the STA (3) 1107, and the STA (4) 1109.

Each of the STA (1) 1103, the STA (2) 1105, the STA (3) 1107, and theSTA (4) 1109 may set the TXOP duration 1130 based on the TXOP settinginformation 1125. In the TXOP duration 1130, data transmission may beperformed between the AP (1) 1101 and each of the STA (1) 1103, the STA(2) 1105, the STA (3) 1107, and the STA (4) 1109 using a method similarto the method described above with reference to FIG. 5.

The STA (1) 1103 to receive data from the AP (1) 1101 may transmit, tothe AP (1) 1101, the response frame 1160 with respect to the TXOPsetting information 1125. The response frame 1160 with respect to theTXOP setting information 1125 may prevent entangling of the STA (1)1103, the STA (2) 1105, the STA (3) 1107, and the STA (4) 1109 whencoverages of a plurality of APs are overlapped with each other.

FIG. 12 illustrates an example of a VHT capabilities element that may beused by an access point to express the access point's power savingsupport capability. It should be appreciated that the terminal may alsouse the VHT capabilities element to express the terminal's power savingsupport capability. For example, the VHT capability information elementmay be included in an association request frame or an associationresponse frame based on the IEEE 802.11 standard.

Referring to FIG. 12, the access point may express a support capabilityof the access point for a power saving mode using VHT capabilitiesinformation field of a VHT capabilities element.

For example, if a MU TXOP PS field 1210 is set to ‘0’, it may indicatethat the access point does not have the power saving support capabilitywith respect to a corresponding terminal. As another example, if the MUTXOP PS field 1210 is set to ‘1’, it may indicate that the access pointhas the power saving support capability with respect to thecorresponding terminal.

FIG. 13 illustrates an example of a VHT control field of a MAC headerthat may be used by a terminal to notify an access point of a powermanagement mode of the terminal.

As described above with reference to FIG. 1, the terminal may operate inthe power management mode such as an active mode corresponding to one ofa non-TXOP PS mode 130, and a TXOP PS mode 140. Accordingly, theterminal may notify the access point of the power management of theaccess point using B29 of a VHT control field. The terminal may alsooperate in the power saving mode 120. Accordingly, the terminal may useone or more bits of the VHT control field to notify the access pointthat the terminal is in power saving mode 120.

When B29 of the VHT control field is set to ‘0’, it may indicate thatthe power management mode of the terminal corresponds to the non-TXOP PSmode. When B29 of the VHT control field is set to ‘1’, it may indicatethat the power management mode of the terminal corresponds to the TXOPPS mode.

FIG. 14 illustrates an example of a VHT-SIG A frame that may be used byan access point to allow a terminal to operate in a power saving mode.

The access point may notify terminals about whether the access pointallows each of the terminal to operate in a power management mode at thebeginning of a downlink MU TXOP duration.

For example, when the access point sets B22 of a VHT-SIG-A field to ‘0’,it may indicate that the access point does not allow the correspondingterminal to operate in the power saving mode. When the access point setsB22 of the VHT-SIG-A field to ‘1’, it may indicate that the access pointallows the corresponding terminal to operate in the power saving mode.

FIG. 15 illustrates an example of a terminal.

Referring to FIG. 15, terminal 1500 includes a receiver 1510, acontroller 1520, a power management unit 1530, and a transmitter 1540.

The receiver 1510 is configured to receive one or more data frames froman access point during a transmission opportunity (TXOP) of the accesspoint. For example, the receiver 1510 may receive a data stream from theaccess point during a TXOP obtained by the access point.

The controller 1520 is configured to determine whether one a of aplurality of criterion is satisfied based on data included in the dataframe received from the access point. For example, the criterion mayinclude the first criterion, the second criterion, and the thirdcriterion described herein with reference to FIGS. 1-14.

The first criterion may be satisfied if the terminal 1500 is not apartof the group of terminals that are served by the access point during theTXOP. For example, a group ID of a data frame may indicate that thecorresponding terminal 1500 is not a member of the group for the TXOP.

In various aspects, the first criterion may not be satisfied. If thegroup ID of the data frame indicates that the corresponding terminal1500 is a member of the group, the second criterion may be satisfied ifthe terminal 1500 is not to receive a data stream during the TXOP. Forexample, a number of state time space (N_(STS)) bit included in a veryhigh throughput signal (VHT-SIG) field of the data frame received fromthe access point may indicate that the terminal 1500 is not going to betransmitted data during the TXOP.

In various aspects, the first and second criterion may not be satisfied.For example, a group ID of the data frame may indicate that the terminal1500 is a member of the group, and a N_(STS) bit included in a VHT-SIGfield of the frame may indicate that the terminal 1500 is to betransmitted data during the TXOP. However, the third criterion may besatisfied if the terminal 1500 is completed receiving a data streamduring the TXOP, and no more data frames are pending for the terminal1500 at the access point. For example, a more data bit (MDB) included ina MAC header of the data frame or of another data frame may indicatethat the transmission of the data from the access point to the terminal1500 is completed for the TXOP.

The power management unit 1530 may be configured to adjust the powermode of the terminal. For example, if the controller 1520 determinesthat any one of the criterion of the plurality of criterion issatisfied, the power management unit 1530 may adjust the power mode ofthe terminal 1500 into a power saving mode for the duration of the TXOP.For example, the power saving mode may be a sleep mode or a doze statefor the duration of the TXOP.

The controller 1520 may be configured to indicate to the access pointthat the terminal is capable of operating in the power saving mode. Forexample, the controller 1520 may set one or more bits of a capabilityelement of a VHT control frame to indicate a power management mode ofthe terminal 1500. For example, referring again to FIG. 1, the VHTcontrol frame may be used to indicate whether the terminal 1500 iscapable of operating in the non-power save (non-PS) TXOP mode 130, inwhich the terminal remains continuously awake, a power save (PS) TXOPmode in 140 which the terminal may switch from an awake state to a dozestate in which the terminal sleeps, and a power save mode 120 in whichthe terminal continuously sleeps.

The transmitter 1540 may be configured to transmit, to an access point,a data frame including the VHT control frame indicating the powermanagement mode of the terminal.

As another example, the terminal 1500 may be configured to notify theaccess point whether the terminal 1500 is operating in the power savemode, the non-TXOP PS mode, or whether the terminal is operating in theTXOP PS mode. For example, the controller 1520 may set one or more bitsof a VHT control field of a MAC header to indicate that the powermanagement mode of the terminal corresponds to the power save mode, thenon-TXOP PS mode, or the TXOP PS mode.

FIG. 16 illustrates an example of an access point.

Referring to FIG. 16, access point 1600 includes a controller 1610 and atransmitter 1620. The controller 1610 may be configured to determinewhether a terminal is included in a TXOP obtained by the access point1600. If the controller 1610 determines that a terminal is included inthe TXOP, the controller 1610 may determine what portion of the TXOP theterminal is apart of.

For example, if the controller 1610 determines that the terminal is notincluded in a group of terminals that the access point 1600 may transmitto during the TXOP, the access point 1600 may notify the terminal thatthe terminal is not included in the group of terminals that the accesspoint 1600 is able to transmit data to during the TXOP. For example, thecontroller 1610 may set a group ID field of a data frame such that thegroup ID field indicates that the terminal is not a member of the groupfor the TXOP. The transmitter 1620 may transmit to the terminal, thedata frame comprising a group ID field that indicates that the terminalis not a member of the group for the TXOP.

As another example, if the controller 1610 determines that the terminalis included in a group of terminals that the access point 1600 is maytransmit to during the TXOP, and that the access point 1600 does nothave data to transmit to the terminal during the TXOP, the access point1600 may notify the terminal that the access point 1600 does not have adata stream to transmit to the terminal during the TXOP. For example,the controller 1610 may set a number of state time space (N_(STS)) bitincluded in a very high throughput signal (VHT-SIG) field of the frameto indicate that the terminal is not going to be transmitted data duringthe TXOP.

The transmitter 1620 may transmit, to the terminal, a data framecomprising a number of state time space (N_(STS)) bit included in a veryhigh throughput signal (VHT-SIG) field of the frame to indicate that theterminal is not going to be transmitted data during the TXOP.

As another example, if the controller 1610 determines that the terminalis included in a group of terminals that the access point 1600 is ableto transmit to during the TXOP, and that the access point 1600 does havedata to transmit to the terminal during the TXOP, the access point 1600may notify the terminal that the access point 1600 has completedtransmission of the data stream to the terminal for that respectiveTXOP. For example, the controller 1610 may set a more data bit (MDB) ofa MAC header to indicate that transmission of data to the terminal iscompleted.

The transmitter 1620 may transmit, to the terminal, a data framecomprising a more data bit (MDB) of a MAC header set to indicate thattransmission of data to the terminal is completed.

It should be appreciated that the examples described with reference toFIGS. 1-14 are also applicable to the terminal 1500 and the access point1600 described with reference to FIGS. 15 and 16. Further descriptionthereof is omitted for concision. According to various aspects, when adata stream to be transmitted to a terminal operating in a power savingmode is absent, it is possible to save a power by maintaining anoperation state of the terminal in a sleep state during a TXOP.

According to various aspects, when a terminal operating in a powersaving mode satisfies a predetermined criterion, it is possible todecrease a power consumption by changing an operation state of theterminal from an awake state to a sleep state.

According to various aspects, terminals that are to operate in a powersaving mode among terminals operating in an active may transmit a framein which a power management mode is set to the power saving mode andthereby be enabled to selectively determine whether to operate in thepower saving mode.

The processes, functions, methods and/or software described above may berecorded, stored, or fixed in one or more computer-readable storagemedia that includes program instructions to be implemented by a computerto cause a processor to execute or perform the program instructions. Themedia may also include, alone or in combination with the programinstructions, data files, data structures, and the like. The media andprogram instructions may be those specially designed and constructed, orthey may be of the kind well-known and available to those having skillin the computer software arts. Examples of computer-readable storagemedia include magnetic media such as hard disks, floppy disks, andmagnetic tape; optical media such as CD ROM disks and DVDs;magneto-optical media such as optical disks; and hardware devices thatare specially configured to store and perform program instructions, suchas read-only memory (ROM), random access memory (RAM), flash memory, andthe like. Examples of program instructions include both machine code,such as produced by a compiler, and files containing higher level codethat may be executed by the computer using an interpreter. The describedhardware devices may be configured to act as one or more softwaremodules that are recorded, stored, or fixed in one or morecomputer-readable storage media, in order to perform the operations andmethods described above, or vice versa. In addition, a computer-readablestorage medium may be distributed among computer systems connectedthrough a network and non-transitory computer-readable codes or programinstructions may be stored and executed in a decentralized manner.

As a non-exhaustive illustration only, the terminal device describedherein may refer to mobile devices such as a cellular phone, a personaldigital assistant (PDA), a digital camera, a portable game console, anMP3 player, a portable/personal multimedia player (PMP), a handhelde-book, a portable lab-top personal computer (PC), a global positioningsystem (GPS) navigation, and devices such as a desktop PC, a highdefinition television (HDTV), an optical disc player, a setup box, andthe like, capable of wireless communication or network communicationconsistent with that disclosed herein.

A computing system or a computer may include a microprocessor that iselectrically connected with a bus, a user interface, and a memorycontroller. It may further include a flash memory device. The flashmemory device may store N-bit data via the memory controller. The N-bitdata is processed or will be processed by the microprocessor and N maybe 1 or an integer greater than 1. Where the computing system orcomputer is a mobile apparatus, a battery may be additionally providedto supply operation voltage of the computing system or computer.

It should be apparent to those of ordinary skill in the art that thecomputing system or computer may further include an application chipset,a camera image processor (CIS), a mobile Dynamic Random Access Memory(DRAM), and the like. The memory controller and the flash memory devicemay constitute a solid state drive/disk (SSD) that uses a non-volatilememory to store data.

A number of examples have been described above. Nevertheless, it shouldbe understood that various modifications may be made. For example,suitable results may be achieved if the described techniques areperformed in a different order and/or if components in a describedsystem, architecture, device, or circuit are combined in a differentmanner and/or replaced or supplemented by other components or theirequivalents. Accordingly, other implementations are within the scope ofthe following claims.

What is claimed is:
 1. A method of operating a terminal, the methodcomprising: receiving a preamble comprising VHT-SIG information from anaccess point; and checking a bit comprised in the VHT-SIG information,wherein the bit indicates whether the access point allows the terminalin a transmission opportunity (TXOP) power save mode to enter a dozestate during a TXOP duration.
 2. The method of claim 1, wherein theVHT-SIG information further comprises a group identifier (ID).
 3. Themethod of claim 1, wherein the VHT-SIG information further comprisesinformation of a number of streams for the terminal (NSTS).
 4. Themethod of claim 1, further comprising receiving, from the access point,power saving information indicating whether the access point supportsthe TXOP power save mode.
 5. A method of operating an access point, themethod comprising: setting a bit indicating whether the access pointallows a terminal in a transmission opportunity (TXOP) power save modeto enter a doze state during a TXOP duration; generating VHT-SIGinformation comprising the bit; and transmitting a preamble comprisingthe VHT-SIG information to the terminal.
 6. The method of claim 5,wherein the VHT-SIG information further comprises a group identifier(ID).
 7. The method of claim 5, wherein the VHT-SIG information furthercomprises information of a number of streams for the terminal (NSTS). 8.The method of claim 1, further comprising transmitting, to the terminal,power saving information indicating whether the access point supportsthe TXOP power save mode.
 9. A terminal comprising: a memory configuredto store one or more instructions; and a processor coupled to thememory, wherein the processor, when executing the one or moreinstructions, is configured to: receive, using a receiver, a preamblecomprising VHT-SIG information from an access point; and checking a bitcomprised in the VHT-SIG information, wherein the bit indicates whetherthe access point allows the terminal in a transmission opportunity(TXOP) power save mode to enter a doze state during a TXOP duration. 10.The terminal of claim 9, wherein the VHT-SIG information furthercomprises a group identifier (ID).
 11. The terminal of claim 9, whereinthe VHT-SIG information further comprises information of a number ofstreams for the terminal (NSTS).
 12. The terminal of claim 9, whereinthe processor is further configured to receive, using the receiver,power saving information indicating whether the access point supportsthe TXOP power save mode.
 13. An access point comprising: a memoryconfigured to store one or more instructions; and a processor coupled tothe memory, wherein the processor, when executing the one or moreinstructions, is configured to: set a bit indicating whether the accesspoint allows a terminal in a transmission opportunity (TXOP) power savemode to enter a doze state during a TXOP duration, generate VHT-SIGinformation comprising the bit, and transmit, using a transmitter, apreamble comprising the VHT-SIG information to the terminal.
 14. Theaccess point of claim 13, wherein the VHT-SIG information furthercomprises a group identifier (ID).
 15. The access point of claim 13,wherein the VHT-SIG information further comprises information of anumber of streams for the terminal (NSTS).
 16. The access point of claim13, wherein the processor is further configured to transmit, using thetransmitter, power saving information indicating whether the accesspoint supports the TXOP power save mode.